Immersion lithography is gaining attention due to improvements in critical dimensions and/or depth of focus that it provides. However, the technology also faces some concerns. For instance, on the one hand an ultra-pure immersion liquid may be advantageous to minimize the appearance of stains when drying areas wetted by the liquid, but on the other hand it may be desirable to include additives in the immersion liquid to influence or create desirable properties. E.g., it may be desirable to include acid components in the immersion liquid to avoid or minimize so-called T-topping or other undesirable effects. T-topping, for instance, may occur when a resist layer on a substrate to be exposed to radiation comes into contact with the immersion liquid and components in the resist (e.g. photo-acid generators) diffuse or dissolve into the immersion liquid. See also EP 1 482 372 A1.
Accordingly, objectives of the invention include providing an immersion liquid comprising one or more additives yet having reduced staining concerns.
Also, objectives of the invention include avoiding or minimizing streaming potential effects caused by the flow of immersion liquid (discussed in more detail infra).